The fabrication of semiconductor devices involves forming electronic components in and on semiconductor substrates, such as silicon wafers. These electronic components may include one or more conductive layers, one or more insulation layers, and doped regions formed by implanting various dopants into portions of a semiconductor substrate to achieve specific electrical properties. Semiconductor devices include transistors, resistors, capacitors, and the like, with intermediate and overlying metallization patterns at varying levels, separated by dielectric materials, which interconnect the semiconductor devices to form integrated circuits.
Field-effect transistors (FETs), such as metal-oxide-semiconductor FETs (MOSFETs), are a commonly used semiconductor device. Generally, a FET has three terminals, e.g., a gate structure, a source region, and a drain region. In some instances, the body of the semiconductor may be considered a fourth terminal. The gate structure is a structure used to control output current, e.g., flow of carriers in the channel portion of a FET, through electrical or magnetic fields. The channel portion of the substrate is the region between the source region and the drain region of a semiconductor device that becomes conductive when the semiconductor device is turned on. The source region is a doped region in the semiconductor device from which majority carriers are flowing into the channel portion. The drain region is a doped region in the semiconductor device located at the end of the channel portion, into which carriers are flowing from the source region via the channel portion and out of the semiconductor device through the drain region.
Semiconductor device fabrication is typically a multiple step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of semiconducting material. Etching is used to remove layers from the surface of a wafer during manufacturing. Etching, in conjunction with lithographic techniques, is used to attack certain areas of a semiconductor surface in order to form recesses in the material or to otherwise remove portions of semiconductor layers where predominantly vertical sides are desired. For many etching steps, part of the wafer is protected from the etchant by a masking material which resists etching.
Also in semiconductor device fabrication, areas in which a metal gate is to exist are often filled with a sacrificial gate material, such as polysilicon, that is later replaced with the metal gate material. The sacrificial gate, also called a dummy gate, holds the position for the metal gate and is better able to withstand the more severe processing conditions so as to prevent damage to metal gate material that would occur if the metal gate material were in place during certain processing.
Semiconductor fins are often used in advanced semiconductor manufacturing technology because of the increased integration levels they provide. When a transistor such as a FinFET is formed, it provides a gate width that may be larger than the gate width of a conventional transistor formed on the same substrate region because the gate structure extends over the top and sides of the fin, all of which serve as channels.
Spacers are constructed on semiconductor devices to form a mask for source/drain implantation, as well as encapsulate and protect the sidewalls of the gate. Some issues may arise with spacers, such as whether they can stay in place after the material to which they are attached is removed, whether the spacer profile is acceptable, and whether the underlying material is attacked by the etch removing the material attached to the spacer. Some of these issues result in higher topography on one side of the spacer than the other.